Close Calls

Listening to a bird’s call when he’s off at a distance in the woods can be quite a different experience than when he is close by. If the song propagates through the forest for some distance, the high-frequency content becomes absorbed by the leaves, leaving the lower frequencies to carry on alone. Some information is lost.

Every now and then, I will be treated by a bird singing out from a perch close to me and I can hear much more in his song. This is more likely to occur in the early morning or at dusk, when competing noise sources (wind, distant airplane, barking dogs, local vehicles) are absent. If I am also still (such as sitting pensively in my outdoor tub), I can hear subtleties in his call that I’d otherwise miss.

When the bird calls from back in the woods, what I tend to hear is a purer sound, more like a clean whistle… it’s a simple call. When he lands nearby and sings out, however, I am amazed at all the additional sounds and complexity I can pick up.

For instance, the distant call of the mourning dove is like a soft, low, pure whistle. It’s a clean, cooing sound. Last evening, however, a dove perched on a branch close by, as he called out. I could hear a breathiness to his call, that gets absorbed when he’s calling from back in the trees. This close-by dove sounded to me like he had a wheeze—as if his air passages were constricted, or he had a bit of a cold. And his melodic “coo” sounded more like a yodel, as if he had flipped into a falsetto voice—whereas it sounds more like a smooth, melodic slur when he’s deep in the woods.

When the bird is close, those softer, high-frequency sounds can be distinguished. A bird may quietly lisp, buzz, whisper, rattle, hiss, whir, and rasp, as part of its call. When he’s close by, all these gentle, high-frequency sounds can be heard. They make his call far more interesting and informative.

When we humans talk (or sing) to each other, most of the information that we hear is contained in the high-frequency subtleties. Consonants create clicking, popping, hissing, and buzzing sounds that convey most of the message. Our throat cavities, lips, tongue, and nasal passages create many inflections that add a wide range of sounds. A bird has none of these sound shapers—his complexity comes from incredibly intricate muscle twitches of his bronchial and syrinx regions, deep in his throat. It’s a simpler sound, but still can be loaded with information.

Birds do manage to accomplish a lot of communication with each other—despite the lack of mouth parts to modulate their song. I’m wondering if all the additional sounds I hear when a bird calls from close by are what they use to relay all that information to each other. What difference might he be signaling if that familiar song of his is preceded by a sift gurgle or rattle, or if he tacks on a bit of a whir or buzz at the end, or even if he has a bit of a cold? I’m sure they are telling each other things that I’m usually missing.